build: Remove -extldflags "-static" from LDFLAGS

Using this flag is actually misleading, as it's ineffective unless
'-linkmode external' is used.
With the current LDFLAGS, whether we get a static build or not is highly
dependent on the arch, on the code being compiled, on the use of cgo or
not, ... but there are no guarantees at all that the build will be
static.

$ go build -ldflags '-s -w -extldflags "-static"' -o routes-controller .
$ ldd routes-controller
linux-vdso.so.1 (0x00007ffd2dcc4000)
libpthread.so.0 => /lib64/libpthread.so.0 (0x00007fb2a4888000)
libc.so.6 => /lib64/libc.so.6 (0x00007fb2a46b9000)
/lib64/ld-linux-x86-64.so.2 (0x00007fb2a48bf000)

$ CGO_ENABLED=0 go build -ldflags '-s -w -extldflags "-static"' -o routes-controller .
$ ldd routes-controller
not a dynamic executable

$ CGO_ENABLED=0 go build -ldflags '-s -w' -o routes-controller .
$ ldd routes-controller
not a dynamic executable

On my machine, the `crc` binary generated by `make cross` dynamically
links to libc regardless of the presence or not of this flag.

Moreover, static linking would require installation of glibc-static on
some arches, but statically linking against glibc is not supported on
some OSes (RHEL8).

This commit removes the `-extldflags "-static"` LDFLAGS from Makefile.
The binaries are unchanged before/after that change (same size, and very
few content differences)

Makefile

@@ -61,7 +61,7 @@ ifdef OKD_VERSION
 endif
 
 # https://golang.org/cmd/link/
-LDFLAGS := $(VERSION_VARIABLES) -extldflags='-static' ${GO_EXTRA_LDFLAGS}
+LDFLAGS := $(VERSION_VARIABLES) ${GO_EXTRA_LDFLAGS}
 
 # Add default target
 .PHONY: default